Power Push Over (PPO)

[mceagle]

alot of CFIs and high-time pilots that have died in PPOs would still be alive and here today.

This must be a USA thing Tim - I don't believe that this is the case in Australia - In fact I cannot think of one experienced pilot that has died through PPO

If you have a machine that is not near CLT then your ability to use 'flying skills' to avoid PPO will depend on a large number of variables such as:
..............Rotorblade properties.

I think that this is a good point that is not stressed enough. I have flown a machine that would apparently fly hands off indefinately, but with a differently set of rotorblades, would immediately break into diverging pitch oscillations as soon as you relaxed the stick. I do not know how you could "rate" the stability of the blades but it should be done before airframe stability tests are carried out.

 

[barnstorm2]

With LTL, PPO occurs when a sudden drop in thrust engine (failures) not opposes no anti-torque to rotor lift behind the center of mass. But it seems to me then that torques PPO should stop automatically because the rotor lift disappears itself during the start PPO.
Do you think that this analysis is correct?

LTL PPO? not possible. I suppose you are talking about the LTL bunt theory discussed by Greg and Doug.

You should know that 1. No gyro I have ever heard of is extreemly LTL
2. It is likely that a LTL gyro would have pitch dampening installed
3. No such accident has ever happened.
4. There is considerable doubt that it could even happen (see Dougs post below)
5. Such a design would be a flaw and the correction should be to fix the machine not try to fix the situation with a pilot.
6 PPO is the #1 killer of gyropilots and passingers not bunts such as this. Statisticly, you should be more conerned about proper training and a good pre-flight.

Udi, my interpretation of Greg's theory....

For example, an extremely LTL gyro with no HS experiences a sudden power failure at high airspeed. It nose drops (a stable response), but, because of low rotor damping and some moderate value of frame MOI, it just keeps going. The rotor loses AOA and therefore thrust. It becomes too weak to arrest the pitchover. The gyro simply goes upside down in a "pure bunt."

I'm not convinced that this is possible with real values of frame MOI, thrustline location and rotor damping, but you can at least make up numbers that might work. I suppose we need a name for this kind of scenario -- diabolis ex machina? One might call it dynamic instability if that name weren't already taken.

I would be sure to understand correctly. With HTL, PPO occurs when a sudden drop in rotor lift (strong downdraft) opposes no anti-torque to thrust. But it seems to me then that PPO could be stopped by stopping quickly the engine. Instead, the pilot pulls instinctively the stick, but this has no effect if the rotor thrust has disappeared. And have perhaps even reverses the effect if the rotor thrust is negative.

No. A PPO once started happens in a fraction of a second. There is no time for a pilot to react and it would be questionable as to weather the change in RPM of the engine/prop would come in time.

In the past some people (including myself) have started discussions and threads on the idea of having an electronic "PPO Detector" that would kill the ignition of the engine in a zero-g situation. However, a reasonable evaluation of the concept reveals that it is more reasonable and fault tolerant to simply change the design of the gyro so that will not PPO.

.

 

[barnstorm2]

This must be a USA thing Tim - I don't believe that this is the case in Australia - In fact I cannot think of one experienced pilot that has died through PPO.

Perhaps, but I thought a few Canadian high time pilots PPOed... but I can't recall the names just now to look them up. Maybe it is a N.America thing?

So no high timers have PPO'ed down under ! that is good news.

.

 

[Heron]

I would like to picture in my mind, negative rotor thrust. Someone kindly explain how it happens, please?
thanks
Heron

 

[Lspav8r]

Are there any videos of an actual PPO in progress? I am sure one has been videotaped somewhere. This would go a long way to show the effect rather than let us try to use our minds eye to understand it. As odd as it is to see a gyro in flight outside of the gyro circles that Im sure video has to be around of an actual PPO/Buntover/PIO somewhere on this planet.

 

[Heron]

This one maybe?
http://www.youtube.com/watch?v=VmOeMTUqp98

 

[brett s]

That one is very deceiving because it's playing in slow motion.

There's video out there of the Pee Wee Judge buntover/torqueover from 1972, but looks like it was removed from Youtube.

 

[Doug Riley]

Jean Claude, I think that the instructors who teach in machines that are prone to PPO do teach the student to cut the throttle when they feel low G.

I taught myself to fly gyros in the early 1970's and I did use this technique on my Bensen and early Air Command machines.

The technique is not necessary or useful in a stable machine such as a Dominator or Gyrobee with proper H-stab. These machines nose up when they encounter a downdraft or other sudden reduction rotor angle of attack. That is, they do not start to PPO.

 

[Steve McGowan]

Wow agin

Wow agin

I've been out here all day, flying and teacing PIO avoidance with every student..

Yall show talkin alott about something so simple to avoid..

Oh well... I jest simple minded I guess..

 

[Heron]

No you ain't, you just teach in a machine that can do the P Dance so you were out training people to recognize it and avoid the situ.
no biggie for ya!
Heron

 

[Doug Riley]

I used to give rides all day at flyins in my tandem Dominator. Day after day.

I'd sit the newbie down in a chair in the shade and we'd do some "pretend" flying for about ten minutes. Once we took off and got to altitude, I would turn the stick over to him/her and put my hands in my lap. More than once I heard over the intercom "You mean I'm really flying this thing?"

In all of those flights with absolute newbies -- grandmas and teenagers and everyone in between -- not one of them ever PIOed the machine. Not one, not for an instant. Porpoising was simply a non-issue.

If the machine is properly designed, PIO is very unlikely. If not, the instructor has to chew up the student's time and money, teaching him to compensate for the designer's poor work.

The choice is yours.

 

[C. Beaty]

It’s a shame you’re not still instructing Doug.

Unfortunately, it’s a helluva way to earn a living. The only CFIs I’m aware of that earned a living as full time gyro flight instructors was Steve Graves and presently, Ron Menzie. I suppose some RAF CFIs did also, before the bubble burst.

 

[Doug Riley]

Chuck, I didn't expect to make a living at it here in the north, where flying is infrequent in the winter. I did expect to cover depreciation, fuel and maintenance -- which didn't happen, either.

The IRS gets unpleasant if you show a loss every year. I kept all the books and paperwork very official-like, for liability reasons.

The FAA's cancellation of the BFI program was the last straw.

 

[Harry_S.]

Ya know what...I'm just wonderin'...

Ya know what...I'm just wonderin'...

Why I, as well as most fix wing pilots, in training, were taught stalls eg, power on & power off, and how to recover from the same, and entry into and the violent result of an accelerated stall.

I'll take a WAG and say that I think it was taught as maybe an added safety factor for any future dalliance or inattention on the part of the aviator...not the particular aircraft he be flyin' at the time. Then again...maybe not.

I like how Steve McGowan does it. Instructs and probably demonstrates actual PIO and how to recover from the PIO. Excellent!!! Simple!!!

I think it a disservice to the student gyro pilot to impress upon him that he need never worry about PIO because he will be flying a Dominator or any other CLT machine and...while flying, NOT impress upon him nor demonstrate PIO and how to recover from same.

NOTICE: I've not mentioned HTL machines: I voiced my concern of the apparent lack of concern about the inherent danger of Progressive PIO, whether it be CLT or HTL.

That's my 2 bits.


Cheers

 

[Doug Riley]

Harry, true PIO is started by the student and amplified by an aircraft that has too little pitch damping. Trouble is, my students never got the Dominator to PIO. It just didn't happen. The thing was damped like it was stuck in mud.

I could have horsed the stick back and forth on them manually, but that would be pretty lame and probably nothing like the real thing. My approach, of necessity, was to refuse to train anyone who was going to transition into an unstable gyro. If they modified it to make it stable, I 'd teach them, but only then.

Greg Gremminger is even stricter than I was about what the student was going to fly. You can't realistically demonstrate instability in a stable aircraft.

The twin fallacies lurking here are (1) all gyros are prone to PIO and (2) beginners ought to be taught test-pilot-level skills.

#2 is, in fact, what the Bensen manual sought to do, with its use of an intentionally unstable "point" trainer (the old auto-brake-drum-universal-joint contraption) and the jab-counter-jab technique. I think this was madness.

My own teaching experience tells me that #1 is simply factually untrue. I was surprised to learn that but, as usual, my students taught me as much as I taught them.

 

[Joe Pires]

Doug I really have to agree with you. In order to teach me how to handle PIO you will need to train in an unstable machine which is capable of developing PIO. I will just as soon fly a stable machine and not have to learn to deal with it.

That is not to say my training is not complete. I won't be trained in water landings either, because it is simply not germain to the aircraft I will be flying.

Should I develop a desire to fly an unstable aircraft, I would expect to train additionally for those new skills I would now need, just as a fixed wing pilot gets new training to handle a plane with new characteristics.

 

[Vance]

Attitude is important.

Attitude is important.

There has been some comparison of power push overs in gyroplanes to stalls in fixed wings. They are both a source of bent aircraft and injured pilots. Some people feel that it is not necessary to practice stalls in a fixed wing because they have got natural flying talent and know how to avoid a stall. They think that they don’t really need to understand how a gyroplane flies because they have natural flying skills.

I don’t like to see people get hurt and I would not feel right with myself if I didn’t say something.

As I read the NTSB reports I see that the most consistently dangerous element is poor aviation decision making that rises out of an attitude that “I am a better pilot than all those that have crashed before me or I will find the skills when I need them.”

I looked at NTSB accident reports where the accident was attributed to stalls in the last ten years and there were 2,241 with 890 fatal.

I suspect that most of them wished they had practiced stalls and identifying the onset of a stall in the moments before they hit the ground.

I feel that a large part of mitigating the risk of aviation is attitude and understanding.

I am grateful for the knowledge I gain here that may help me to make better aviation decisions.

Poor aviation decisions will usually not result in a negative outcome and many use this experience to justify additional poor aviation decisions. In my opinion, this exacerbates the risks inherent in manned flight.

I hope that all my friends here on the forum will learn all they can about how things fly and continue to enhance their flying skills so they will not show up on the NTSB reports.

Thank you, Vance

 

[Resasi]

Vance a member of the Forum posted this which I thought summed it up very well. I apologize to him for forgetting his name.

A pilot may pick up the performance of physical tasks quicker than most others. But it is no substitute for experience. There is no shortcut to experience. The reason why we don't turn the car over to a 14 year-old is not that they are incapable of sitting behind the wheel and making the car go. They can start it, put it in gear, turn the wheel, etc. But they lack judgement and experience. Some, stress some, judgement will come with experience. A lot of it comes with well explained instruction. The purpose of instruction is not just to get you in the air, or on the road, and back. It is to help you understand what you are doing and why and to prepare you for situations that may not specifically be covered in everyday operations. Nobody wants to "waste" money on un-needed instruction. But good preparation saves money in the long run. Repairs and funerals are expensive, too.

 

[Harry_S.]

Thank you Vance and Leigh. Good posts.


Doug,

The machine don't PIO...the PILOT does.

I find it hard to believe that when flying your Dominator, you cannot simulate PIO. PIO is the result of over control inputs, correct?

Can you not when flying S/L at cruise power, pull full aft stick and hold it till the nose reaches for the sky...then give it full fwd. stick and hold it till the nose dives toward the ground...then full aft stick again? Would this not simulate PIO?

A verbal or text book description of a fully developed "spin" of a fixed wing aircraft is nothing as compared to the mental/visual impact of the practical experience of the same. Well, to me it wasn't the first time.

The practical demonstration of PIO, as described, would be no problem in the pitch stable Dominator...should it?! IMO, it would be most beneficial to the student.


Cheers

 

[Doug Riley]

Yeah, Harry, you can do that, but I'm not sure what it would teach the student. The part of PIO that the student needs to experience IMHO is the rhythm of it -- the sneaky way that oscillations build up when you think you're doing all the right things. The Dom just doesn't do that, though my Air Command would.

The students did do the kind of non-rhythmic over-control that you describe, on their own. I would talk them through it or give the stick a bump in the right direction.

All ancient history now. These days, I teach sailing instead. You can PIO sailboats, too.